Paint is any liquid, liquefiable, or mastic composition which, after application to a substrate in a thin layer, is converted to a solid film. It is most commonly used to protect, color or provide texture to objects. Paint contains a binder (also known as a vehicle or resin), a diluent or solvent, a pigment or filler, and may also have other additives. The binder, commonly called the vehicle, is the film-forming component of paint. It is the only component that must be present. Components listed below are included optionally, depending on the desired properties of the cured film.
The binder imparts adhesion and strongly influences such properties as gloss, durability, flexibility, and toughness. In latex paint the binder comprises latex.
Latex is a stable dispersion (colloidal emulsion) of polymer microparticles in an aqueous medium. Thus, it is a suspension/dispersion of rubber or plastic polymer microparticles in water. Latexes may be natural or synthetic. Polymerization is a preferred technology used to make emulsion polymers and polymer latexes.
Latex paint is a water-borne dispersion of sub-micrometer polymer particles. The term “latex” in the context of paint simply means an aqueous dispersion; latex rubber (the sap of the rubber tree that has historically been called latex) is not an ingredient. The use of latex, produced by emulsion polymerization, in the production of paints or coatings for substrates is well known in the art.
Three categories of polymers produced by emulsion polymerization are: (1) Synthetic rubber: some grades of styrene-butadiene (SBR), Some grades of polybutadiene, polychloroprene (Neoprene), nitrile rubber, acrylic rubber, fluoroelastomer (FKM); (2) Plastic: Some grades of PVC, some grades of polystyrene, some grades of PMMA (polymethylmethacrylate), Acrylonitrile-butadiene-styrene terpolymer (ABS), polyvinylidene fluoride, polytertrafluoroethylene (PTFE); and (3) Dispersions (polymers sold as aqueous dispersions, for example, latex).
Latex paints are used for a variety of applications including interior and exterior, and flat, semi-gloss and gloss applications. Latex polymer binder is a latex polymer which coalesces to form a film. Latex paints cure by a process called coalescence where first the water, and then the trace, or coalescing, solvent, evaporate and draw together and soften the latex polymer binder particles and fuse them together into irreversibly bound networked structures, so that the paint will not redissolve in the solvent/water that originally carried it. This is a characteristic of paints which distinguishes from, for example, aqueous desktop inkjet printer inks. However, such paints or coatings are adversely affected by the presence of emulsifiers required in the emulsion polymerization process. Furthermore, in latex polymerization, surfactants are necessary to provide stable monomer pre-emulsion, stability during the polymerization, and overall stability of the final latex. The residual surfactants in paint as well as hydrolytic effects with some polymers may cause the paint to remain susceptible to softening and, over time, degradation by water.
The main purposes of the diluent are to dissolve the polymer and adjust the viscosity of the paint. It is volatile and does not become part of the paint film. It also controls flow and application properties, and in some cases can affect the stability of the paint while in liquid state. Its main function is as the carrier for the non volatile components. To spread heavier oils (for example, linseed) as in oil-based interior house paint, a thinner oil is required. These volatile substances impart their properties temporarily—once the solvent has evaporated, the remaining paint is fixed to the surface. This component is optional: some paints have no diluent. Water is the main diluent for water-borne paints, even the co-solvent types. Solvent-borne, also called oil-based, paints can have various combinations of organic solvents as the diluent, including aliphatics, aromatics, alcohols, ketones and white spirit. Specific examples are organic solvents such as petroleum distillate, esters, glycol ethers, and the like. Sometimes volatile low-molecular weight synthetic resins also serve as diluents.
Pigments are granular solids incorporated in the paint to contribute color. Fillers are granular solids incorporate to impart toughness, texture, give the paint special properties, or to reduce the cost of the paint. Alternatively, some paints contain dyes instead of or in combination with pigments. Pigments can be classified as either natural or synthetic types. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas. Hiding pigments, in making paint opaque, also protect the substrate from the harmful effects of ultraviolet light. Hiding pigments include titanium dioxide, phthalo blue, red iron oxide, and many others. Fillers are a special type of pigment that serve to thicken the film, support its structure and increase the volume of the paint. Fillers are usually cheap and inert materials, such as diatomaceous earth, talc, lime, barytes, clay, etc. Floor paints that will be subjected to abrasion may contain fine quartz sand as filler. Not all paints include fillers. On the other hand, some paints contain large proportions of pigment/filler and binder.
Besides the three main categories of ingredients, paint can have a wide variety of miscellaneous additives, which are usually added in small amounts, yet provide a significant effect on the product. Some examples include additives to modify surface tension, improve flow properties, improve the finished appearance, increase wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, UV stabilizers, flatteners (de-glossing agents), biocides to fight bacterial growth, and the like. Additives normally do not significantly alter the percentages of individual components in a formulation
In the paints and coatings additives market, surfactants and biocides are important components in a formulation for various reasons. Surfactants are used as wetting, anti-foaming and dispersing agents. Biocides are used for controlling microbes from spoilage and protect dry films from mildew growth.
Biocides and mildewcides are two classes of antimicrobial agents used in a can of paint for two main goals. Biocides, also known as in-can preservatives, are used to preserve wet paints from spoilage due to bacterial growth whereas mildewcides are used to protect dry films from fungal deteriorations. Biocides belonging to different classes of chemistries such as formaldehyde releasers, isothiazolinones, carbamates and thiols are used for their various properties. Some of the chemistries are either listed as carcinogens or are corrosive and sensitizers.
Dry film fungicides or mildewcides usage has recently increased for interior paints since the year 2000, because of the flooding and building damages due to hurricane Katrina in the New Orleans. Interior paints in homes for basements, bathrooms and kitchens, in hotel rooms, school buildings and hospital environments are being formulated with mildewcides that are not environmentally friendly or have issues of handling safety and causing sensitizing reactions.
Use of environmentally friendly chemicals in the industry is gaining significance in the current environment of “green” chemistry and sustainability. Surfactants are key ingredients of many formulations in various applications.
Paints and inks are two different categories of products. For example, desktop inkjet printers, as used in offices or at home, tend to use aqueous inks based on a mixture of water, glycol and dyes or pigments. These inks are inexpensive to manufacture, but are difficult to control on the surface of media, often requiring specially coated media. Some desktop inks contain sulfonated polyazo black dye (commonly used for dying leather), nitrates and other compounds. Aqueous inks are mainly used in printers with thermal inkjet heads, as these heads require water to perform. While aqueous inks often provide the broadest color gamut and most vivid color, most are not waterproof without specialized coating or lamination after printing. Most Dye-based inks, while usually the least expensive, are subject to rapid fading when exposed to light. Pigment-based aqueous inks are typically more costly but provide much better long-term durability and ultraviolet resistance. Inks marketed as “Archival Quality” are usually pigment-based.
Surfactants can be classified according to the nature of the charge on individual polar moiety. Anionic surfactants are negatively charged usually due to a sulphonate or sulphur group. Non-ionic surfactants lack ionic constituent and the majority of all non-ionics are polymerization products of 1,2-epoxyethane. Cationic surfactants are characterized by a quaternary ammonium group which is positively charged. Lastly, amphoteric surfactants have both positively and negatively charged moieties in the same molecule. Biosurfactants can also be grouped into two categories namely, (1) low-molecular-mass molecules with lower surface and interfacial tensions and (2) high-molecular-mass polymers which bind tightly to surfaces. Examples of low-molecular-mass molecules are rhamnolipids and sophorolipids. Examples of high molecular-mass polymers are food emulsifiers and biodispersants.